Freezing a sacrificial material in forming a semiconductor

ABSTRACT

The present disclosure includes apparatuses and methods related to freezing a sacrificial material in forming a semiconductor. In an example, a method may include solidifying, via freezing, a sacrificial material in an opening of a structure, wherein the sacrificial material has a freezing point below a boiling point of a solvent used in a wet clean operation and removing the sacrificial material via sublimation by exposing the sacrificial material to a particular temperature range.

PRIORITY INFORMATION

This application is a Continuation of U.S. application Ser. No.15/847,705, filed on Dec. 19, 2017, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor processing,and, more particularly, to freezing a sacrificial material in forming asemiconductor.

BACKGROUND

Semiconductor processing (e.g., fabrication) can be used to formsemiconductor devices, such as integrated circuits, memory devices,microelectromechanical devices (MEMS), etc.

Examples of memory devices that can be formed by semiconductorprocessing include, but are not limited to, volatile memory (e.g., thatcan require power to maintain its data), such as random-access memory(RAM), dynamic random access memory (DRAM), synchronous dynamic randomaccess memory (SDRAM), among others, and non-volatile memory (e.g., thatcan provide persistent data by retaining stored data when not powered),such as NAND flash memory, NOR flash memory, read only memory (ROM),electrically erasable programmable ROM (EEPROM), erasable programmableROM (EPROM, among others.

Semiconductor processing can involve forming features (e.g., patterns)on and/or in a semiconductor (e.g., of silicon) that may be referred toas a wafer or substrate. In some examples, one or more materials, suchas silicon-based materials (e.g., silicon oxide (SiO), silicon nitride(SiN), tetraethyl orthosilicate (TEOS), and/or polysilicon) may beformed on the semiconductor. For instance, a deposition process, such asphysical vapor deposition (PVD), chemical vapor deposition (CVD), atomiclayer deposition (ALD), electrochemical deposition and/or molecular beamepitaxy, among others may be used to form one or more materials on thesemiconductor.

Subsequently, portions of the one or more materials, and in someinstances, portions of the semiconductor, may be removed, such as by wetand/or dry etching, to form the features. In some examples, the featuresmay have high aspect ratios (e.g., ratio of height to width or diameter)and may be referred to as high-aspect-ratio (HAR) features. For example,the features might be separated from each other by HAR openings.

During processing, the semiconductor and the features may be subjectedto wet processing, such as wet cleaning, and subsequent drying. Forexample, wet cleaning can be helpful to remove residue left behind, suchas by the removal process or other processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents various examples of feature toppling.

FIGS. 2A-2D illustrate cross-sectional views of processing stepsassociated with forming a semiconductor device, in accordance with anumber of embodiments of the present disclosure.

FIG. 3 an example of a processing step associated with forming asemiconductor device, in accordance with a number of embodiments of thepresent disclosure.

FIG. 4 is a block diagram illustration of a processing apparatus used inconjunction with the processing steps associated with forming asemiconductor device, in accordance with a number of embodiments of thepresent disclosure.

FIG. 5 is a block diagram illustration of an apparatus formed, at leastin part, in accordance with a number of embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The present disclosure includes processing methods associated withforming semiconductor devices, such as integrated circuits, memorydevices MEMS, among others. An example of forming semiconductor devicescan include solidifying, via freezing, a sacrificial material in anopening of a structure, wherein the sacrificial material has a freezingpoint below a boiling point of a solvent used in a wet clean operationand removing the sacrificial material via sublimation by exposing thesacrificial material to a particular temperature and pressure range.

Embodiments of the present disclosure provide technical advantages, suchas reducing the likelihood of feature collapse (e.g. toppling) duringprocessing compared to previous approaches. For instance, a number ofembodiments form a sacrificial material in openings between features ina structure, such as a structure to be used in a semiconductor device(e.g., a memory device), that acts to prevent feature collapse (e.g.,sometimes referred to as pattern collapse) while the structure is dryingat the end of a wet clean operation or while the structure is beingmoved from one processing tool to another processing tool duringprocessing (e.g., formation of the semiconductor device).

Some prior approaches can include forming features in a structure at adry etch tool, such as by dry etching, and moving the structure to a wetcleaning tool (e.g., to clean residue from the dry etch from thestructure). After cleaning, solvent from the wet cleaning tool mayremain on the structure.

For instance, liquid solvent can remain on surfaces of a structure.Remaining liquid solvent can be a problem for structures having highaspect ratio structures, such as shallow trench isolation (STI)structures. For example, the liquid solvent may form in the openingsbetween the features. High surface tension forces may result from theliquid in the openings that can cause the features to topple (e.g.,collapse) toward each other, bringing adjacent features into contactwith each other. For example, FIG. 1 illustrates a feature 101 toppling(e.g., collapsing) into an adjacent feature and a pair of adjacentfeatures 102 toppling into each other (e.g. in what is sometimesreferred to as bridging). This can lead to defects in the semiconductordevice structure, and can even render the semiconductor deviceinoperable.

The sacrificial materials of the embodiments described herein obstructthe openings to prevent liquid solvent from remaining on the high aspectratio structures and in the openings after a wet clean operation, andthus can reduce the likelihood of (e.g., eliminate) high aspect ratiofeatures collapsing due to capillary forces created by the liquidsolvent. The sacrificial material can completely or partially fill theopenings to prevent liquid solvent from remaining in the openings whilethe structures are drying. The sacrificial material can be a eutecticmixture, a hypereutectic composition, and/or a hypoeutectic compositionto form a sacrificial material that is a solid at room temperature, hasa high vapor pressure for sublimation, and has a freezing point belowthe boiling point of the solvent.

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown, byway of illustration, specific examples. In the drawings, like numeralsdescribe substantially similar components throughout the several views.Other examples may be utilized and structural and electrical changes maybe made without departing from the scope of the present disclosure. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present disclosure is defined onlyby the appended claims and equivalents thereof.

The term semiconductor can refer to, for example, a bulk material, asemiconductive wafer, or a substrate, and includes any basesemiconductor structure. “Semiconductor” or “Semiconductive” is to beunderstood as including silicon-on-sapphire (SOS) technology,silicon-on-insulator (SOI) technology, thin-film-transistor (TFT)technology, doped and undoped semiconductors, epitaxial layers of asilicon supported by a base semiconductor structure, as well as othersemiconductor structures. Furthermore, when reference is made to asemiconductor in the following description, previous process steps mayhave been utilized to form regions/junctions in the base semiconductorstructure, and the term semiconductor can include the underlying layerscontaining such regions/junctions. The apparatus can be formed bysemiconductor processing, but are not limited to semiconductor orsemiconductive structures. For example, the apparatus can be formedusing quartz substrate and/or other materials.

The figures herein follow a numbering convention in which the firstdigit or digits correspond to the drawing figure number and theremaining digits identify an element or component in the drawing.Similar elements or components between different figures may beidentified by the use of similar digits. For example, 211 may referenceelement “11” in FIG. 2A, and a similar element may be referenced as 311in FIG. 3. As will be appreciated, elements shown in the variousembodiments herein can be added, exchanged, and/or eliminated so as toprovide a number of additional embodiments of the present disclosure. Inaddition, as will be appreciated, the proportion and the relative scaleof the elements provided in the figures are intended to illustrate theembodiments of the present disclosure, and should not be taken in alimiting sense.

FIGS. 2A-2D illustrate cross-sectional views of processing stepsassociated with forming a semiconductor device, such as a portion of anintegrated circuit, a memory device, a MEMS, among others, in accordancewith a number of embodiments of the present disclosure. For example, theprocessing steps may be associated with forming (e.g., a memory arrayof) a DRAM memory device, a NAND flash memory device, a NOR flash memorydevice, among others.

FIG. 2A depicts a structure (e.g., to be used in a semiconductor device)after several processing steps have occurred. The structure may includea base structure, such as a substrate 206 (e.g., a semiconductor). Insome examples, one or more materials 210, such as silicon-based ornon-silicon based materials, may be formed on (e.g., over) a surface208, such as an upper surface, of semiconductor 206, using, for example,a deposition process, such as PVD, CVD, ALD, electrochemical depositionand/or molecular beam epitaxy, among others.

Features 211, such as microfeatures (e.g., having a width or diameter ofabout 0.1 micrometer to about 100 micrometer) and/or nanofeatures (e.g.,having a width or diameter of about 0.1 nanometer to about 100nanometer) are formed by removing portions of the structure, such asportions of the one or more materials 210 and portions of semiconductor206. The removal process forms openings 212, such as spaces (e.g.,trenches), through the one or more materials 210, stopping on or in(e.g., as shown in FIG. 2A) semiconductor 206. For example, an opening212 may be between adjacent features 211. In some examples, each of therespective features 211 includes the one or more materials 210 and aportion of semiconductor 206. In some instances, the removal process canstop above or on the surface of substrate 206.

In some examples, portions of the openings 212 in semiconductor 206(e.g., below surface 208) may correspond to isolation regions, such asshallow trench isolation (STI) regions and/or high aspect ratio featuressuch as those used while forming capacitors, transistors, and otherelectrical components. In an example, a feature 211 may be entirely ofsemiconductor 206, and openings 212 may correspond to STI regions.Features 211 may be HAR features, and openings 212 may be HAR openings.For example, an HAR may have a height to width or diameter ratio of 10to 1, 25 to 1, or greater.

In some examples, openings 212, and thus the structure in FIG. 2A, maybe formed using a dry processing tool (not shown), such as the dryremoval tool (e.g., dry etch tool), using a dry removal process, such asa dry etch. A mask (not shown), such as imaging resist (e.g.,photo-resist), may be formed over the one or more materials 210 andpatterned to expose regions of the one or more materials 210. Theexposed regions may be subsequently removed, such as by the dry etchprocess, to form openings 212 that may terminate on or in semiconductor206.

In some examples, material, such as a dielectric material (e.g., siliconoxide, silicon nitride, etc.), an organic compound (e.g., an organicpolymer), an ionic compound (e.g., an ammonium salt or a halide salt), asoluble material (e.g., soluble in a solvent, such as water,hydrofluoric acid (HF), etc.), among others, can be formed on thestructure of FIG. 2A to obstruct openings 212. The material may beformed on the structure of FIG. 2A at a dry removal tool before thestructure is exposed to a moisture-containing atmosphere, such as air,for example.

A wet cleaning tool may be dedicated to the removal of the particlesand/or residues that may form as a result of the dry etch and/or toremove other material deposited (e.g., sacrificial material and/or maskmaterial) on the wafer. In some examples, the composition of thematerial used to fill openings may be selected so it can be removed bythe wet clean chemistry to be used for wet cleaning.

Material from the dry-etch process, can be removed from the structurevia the wet cleaning tool (e.g., as part of the wet cleaning operation)to re-expose (e.g., reopen) the openings 212 between features 211. In anexample, the wet cleaning operation may be performed in an inertatmosphere so that the structure of FIG. 2A is not exposed to a reactivegas (e.g., O₂).

In some examples the wet cleaning may include an aqueous wet clean thatmay include hydrofluoric acid (HF). In an example, an aqueous wet cleanmay include a standard clean-1 (SC-1) (e.g. for removing organics,particles, and films) that may include deionized (DI) water, aqueousammonium hydroxide, and aqueous hydrogen peroxide. In some instances, astandard clean 2 (SC-2) (e.g., for removing metal ions) that may includedeionized (DI) water, aqueous hydrochloric acid, and aqueous hydrogenperoxide may be performed after SC-1 as part of the aqueous wet clean.The wet-cleaning process may further include the aqueous wet clean witha DI water rinse, followed by an isopropyl (IPA) rinse, followed bydrying, such as spin drying. In other examples, the wet cleaningoperation and the removal of the material may be integrated, and the wetcleaning operation may remove residue from the dry etch.

Subsequently, as shown in FIG. 2B, a sacrificial material 220, such as avolatile solid material, is formed on (e.g., is used to coat) thestructure of FIG. 2A at the wet cleaning tool, to obstruct openings 212(e.g., without exposing the structure to a gas). For example,sacrificial material 220 may be spin coated onto the structure of FIG.2A. In some examples, sacrificial material 220 obstructs openings 212 bycompletely filling openings 212. In some examples, sacrificial material220 can completely fill openings 212 such that an upper surface ofsacrificial material 220 may be coplanar (e.g., flush) with the uppersurfaces 216 of features 211. Additionally, as shown in FIG. 2B,sacrificial material 220 can overfill openings 212 and extend over(e.g., cover) upper surfaces 216 of features 211. In some examples,sacrificial material 220 may partially fill openings 212 such that theupper surface of sacrificial material 220 may be below the level ofupper surface 216. In some examples, sacrificial material 220 maycompletely displace any liquid from the wet cleaning operation.

In some examples, the volatile solid may be melted to create a liquid.The liquid can then be deposited on the structure of FIG. 2A and intothe openings 212 in FIG. 2A and solidified to form the structure of FIG.2B. The liquid can be solidified via freezing, for example.

Subsequently, the structure of FIG. 2B can be moved from the wetcleaning tool to a different processing tool, such as the depositiontool. For example, the structure of FIG. 2B may be exposed to amoisture-containing atmosphere as it is moved from the wet cleaning toolto the deposition tool. However, by closing openings 212 and coveringfeatures 211, sacrificial material 220 prevents condensation on thefeatures 211 and in openings 212, and thus the toppling of features 211resulting from the condensation and/or physical forces. Sacrificialmaterial 220 may also protect features 211 from oxidation that can occuras the structure is being moved through an oxygen containing atmosphere.

As shown in FIG. 2C, sacrificial material 220 may be removed at the wetcleaning tool and/or deposition tool to re-expose openings 212 betweenfeatures 211. For examples in which sacrificial material 220 is avolatile material, sacrificial material 220 may be removed bysublimation. For instance, the pressure, temperature, and/or gas in achamber, such as chamber 440 as shown in FIG. 4, may be set such thatsacrificial material 220 sublimates. For example, the pressure may becontrolled by a pump 444 as shown in FIG. 4, temperature may becontrolled by a temperature control 443, and gas inside chamber may becontrolled by a gas purge 446 as shown in FIG. 4. In other examples, thevolatile sacrificial material 220 may be removed by removing thestructure from the chamber. The sacrificial material 220 can be aeutectic mixture, a hypereutectic composition, and/or a hypoeutecticcomposition to form a sacrificial material 220 that is a solid at roomtemperature, has a high vapor pressure for sublimation, and has afreezing point below the boiling point of the solvent.

In some examples, openings 212 in the structure of FIG. 2A may beobstructed without completely filling openings 212 with a sacrificialmaterial, such as sacrificial material 220 in FIG. 2B. As shown in FIG.3, a sacrificial material 330 may be formed on a structure, such as thestructure of FIG. 2A, to form the structure in FIG. 3. Sacrificialmaterial 330 is formed in openings 312 and between features 311 so thatsacrificial material 330 obstructs the openings 312 adjacent to a top ofthe openings 312 without completely filling the openings 312.Sacrificial material 330 pinches off adjacent to the top of the openingsbefore the openings are completely filled, leaving voids 332 betweenfeatures 311. For example, sacrificial material 330 lines openings 312and obstructs openings 312 adjacent to the tops of openings 312 tocreate voids 332. For instance, the sacrificial material 330 is coupledbetween adjacent features 311 by spanning upper portions of the openingsbetween the adjacent features 311.

In some examples, sacrificial material 330 may be sacrificial material220, such as a volatile material, and the structure of FIG. 3 may beformed at the wet cleaning tool, which can include chamber 440. Forexample, in the case of sacrificial material 330 being a volatilematerial, the sacrificial solid 330 may be removed by sublimation toform the structure of FIG. 2C, as described previously. In someexamples, the structure of FIG. 3 may be formed by applying the volatilesolid as a liquefied solid and allowing the liquefied solid to solidify.

In other examples, sacrificial material 330 may be deposited topartially fill openings 312 such that sacrificial material 330 is formedon features 311 within openings 312, as shown in FIG. 3, thus liningopenings 312, but without pinching off.

FIG. 4 is a block diagram illustration of a processing apparatus used inconjunction with the processing steps associated with forming asemiconductor device, in accordance with a number of embodiments of thepresent disclosure. The processing apparatus can include a chamber 440to form sacrificial material in openings of structures, a carrier 442can hold a batch of semiconductor wafers 443, and tools, for example apump 444, a gas purge 446, and a temperature control 448, can removesacrificial material via sublimation.

In some examples, a sacrificial material can be formed in an opening ofa structure in the chamber 440. The sacrificial material can obstructthe opening 212 in FIG. 2A or 2C, in the structure. The structure can beincluded on one of the semiconductor wafers 443. The structure caninclude a plurality of features. The sacrificial material in a solidstate can prevent pattern collapse caused by capillary forces after wetclean operations.

In some examples, the sacrificial material can be formed in the openingof the structure in response to performing a wet clean operation. Thewet clean operation can be performed in chamber 440 and/or the sameapparatus as the chamber 440 is in. The wet clean operation can includeusing a solvent to wet clean the structure prior to forming thesacrificial material. The solvent can evaporate prior to removing thesacrificial material. The solvent can evaporate in a carbon dioxide(CO₂) atmosphere, for example. In some examples, the sacrificialmaterial in liquid state can displace a solvent of the wet cleanoperation. The sacrificial material can be spin coated into the opening212 in FIG. 2A or 2C, in the structure.

In some examples, the sacrificial material can be solidified in theopening of the structure via freezing. Solidifying the sacrificialmaterial can obstruct the opening of the structure. Solidifying caninclude cooling the sacrificial material below its freezing point. Thesacrificial material can be cooled by reducing the temperature of thechamber 440 via a temperature control mechanism 448 of the chamber 440.

In some examples, the freezing point of the sacrificial material can beabove room temperature to allow the sacrificial material to be appliedhot and then freeze at room temperature. The freezing point of thesacrificial material above room temperature prevents the need to coolthe structure and allows the sacrificial material to remain in theopening of the structure at room temperature without melting untilsublimation. The freezing point of the sacrificial material can be abovea temperature at which sublimation occurs to prevent sublimation fromoccurring while the structure is drying. The freezing point of thesacrificial material can be below a boiling point of the solvent toprevent the solvent from boiling when the sacrificial material isprovided. Vapor bubbles can be created and result in collapse caused bycapillary forces when a solvent boils. For example, the freezing pointof the sacrificial material can be below 82 degrees Celsius, the boilingpoint of isopropyl alcohol (IPA). In some examples, the freezing pointof the sacrificial material can be between 30 and 60 degrees Celsius,which is a region above room temperature and below the boiling point ofa solvent.

In some examples, the sacrificial material can be a eutectic mixture, ahypereutectic composition, and/or a hypoeutectic composition to form asacrificial material that is a solid at room temperature, has a highvapor pressure for sublimation, and has a freezing point below theboiling point of the solvent. For example, the sacrificial material canbe a camphor and naphthalene mixture.

The sacrificial material can be removed in the chamber 440. Thesacrificial material can be removed via sublimation by increasing thetemperature of the chamber 440 via the temperature control mechanism 448of the chamber 440. Heating the structure can cause the sacrificialmaterial to thermally decompose into a gaseous product without melting.The structure can be heated using a temperature control 448, for examplea hot plate. The chamber 440 and/or temperature control 448 can includea gas purge 446 or a pump 444, for example a vacuum, to remove thegaseous byproducts. The gas purge 446 and pump 444 can be provided toprotect the structure from oxidation by removing the gaseous byproducts.

In some examples, the sacrificial material can be removed viasublimation by exposing the sacrificial material to sub-atmosphericpressure. The sacrificial material can be exposed to sub-atmosphericpressure via a pump 444 pressurizing the chamber 440. The pump 444 canbe a vacuum connected or separate from the chamber 440, for example. Insome examples, sublimation can be accelerated by heating the structure.The structure can be heated by a temperature control 448, for example.

In some examples, the sacrificial material can be removed viasublimation by removing a reactive gas from the structure. Thesacrificial material can decompose into a gas mixture in response toremoving the reactive gas from the structure. The reactive gas can beremoved via the gas purge 446, for example.

FIG. 5 is a block diagram of an apparatus, such as a memory device 550.For example, memory device 550 may be a volatile memory device, such asa DRAM, a non-volatile memory device, such as NAND flash or NOR flash,among others. For example, memory device 550 may be formed, at least inpart, using the processing previously described, such as in conjunctionwith FIGS. 2A-2D and FIG. 3.

Memory device 550 includes a controller 552, such as an applicationspecific integrated circuit (ASIC), coupled to a memory array 554, suchas a DRAM array, a NAND array, a NOR array, among others. For example,memory array 454 might be formed, at least in part, according to theprocessing described previously.

The controller 552 can control the operations on the memory device 550,and of the memory array 554, including data sensing (e.g., reading) anddata programming (e.g., writing), for example. Memory device 550 may becoupled to a host device (not shown in FIG. 5).

Embodiments of the disclosure use sacrificial materials to obstructopenings in structures (e.g., to be used in semiconductor devices, suchas integrated circuits, memory devices, MEMS, and the like), such asbetween features in the structures. The sacrificial materials preventcondensate from forming in the openings as the structures are movedthrough a moist atmosphere between tools, thereby preventing thefeatures from collapsing.

Although specific examples have been illustrated and described herein,those of ordinary skill in the art will appreciate that an arrangementcalculated to achieve the same results may be substituted for thespecific embodiments shown. This disclosure is intended to coveradaptations or variations of one or more embodiments of the presentdisclosure. It is to be understood that the above description has beenmade in an illustrative fashion, and not a restrictive one. The scope ofone or more examples of the present disclosure should be determined withreference to the appended claims, along with the full range ofequivalents to which such claims are entitled.

What is claimed is:
 1. A method for forming a semiconductor device,comprising: displacing a solvent, used in a wet clean operation, in anopening of a structure with a sacrificial material at a wet cleaningtool; solidifying the sacrificial material in the opening of thestructure; and removing the sacrificial material via sublimation byexposing the sacrificial material to a particular temperature range at adeposition tool.
 2. The method of claim 1, further comprisingsolidifying, via freezing, the sacrificial material in the opening ofthe structure by reducing a temperature of the sacrificial material toless than a freezing point temperature of the sacrificial material. 3.The method of claim 2, wherein the freezing point temperature of thesacrificial material is less than a boiling point temperature of thesolvent used in the wet clean operation.
 4. The method of claim 2,wherein the freezing point temperature of the sacrificial material isgreater than room temperature.
 5. The method of claim 2, wherein thefreezing point temperature of the sacrificial material is less than 82degrees Celsius.
 6. The method of claim 2, wherein the freezing pointtemperature of the sacrificial material is between 30 and 60 degreesCelsius.
 7. The method of claim 2, wherein the freezing pointtemperature of the sacrificial material is less than a boiling pointtemperature of isopropyl alcohol (IPA).
 8. A method for forming asemiconductor device, comprising: forming a plurality of features in astructure at a dry etch tool; performing a wet clean operation on thestructure using a solvent at a wet cleaning tool; displacing the solventwith a sacrificial material at the wet cleaning tool; solidifying thesacrificial material in openings of the plurality of features at the wetcleaning tool; and removing the sacrificial material via sublimation byexposing the sacrificial material to a particular temperature range at adeposition tool.
 9. The method of claim 8, wherein solidifying thesacrificial material obstructs the openings of the plurality offeatures.
 10. The method of claim 8, wherein the sacrificial materialincludes camphor.
 11. The method of claim 8, wherein the sacrificialmaterial includes naphthalene.
 12. The method of claim 8, wherein thesacrificial material is a camphor and naphthalene mixture.
 13. Themethod of claim 8, wherein solidifying the sacrificial material preventspattern collapse while the plurality of features dry.
 14. A method forforming a semiconductor device, comprising: displacing a solvent, usedin a wet clean operation, in an opening of a structure with asacrificial material at a wet cleaning tool; solidifying the sacrificialmaterial in the opening of the structure; exposing the structure withthe sacrificial material to oxygen after solidifying the sacrificialmaterial and prior to removing the sacrificial material in response tomoving the structure from the wet cleaning tool to a deposition tool;and removing the sacrificial material via sublimation by exposing thesacrificial material to a particular temperature range at the depositiontool.
 15. The method of claim 14, wherein the solvent is isopropylalcohol (IPA).
 16. The method of claim 14, wherein a temperature of thesacrificial material is greater than room temperature when thesacrificial material is displacing the solvent.
 17. The method of claim14, further comprising: thermally decomposing the sacrificial materialinto a gaseous byproduct in response to exposing the sacrificialmaterial to the particular temperature range; and removing the gaseousbyproduct to protect the structure from oxidation.
 18. The method ofclaim 14, further comprising exposing the sacrificial material to aparticular pressure range.
 19. The method of claim 18, furthercomprising removing the sacrificial material via sublimation by exposingthe sacrificial material to the particular temperature range and theparticular pressure range at the deposition tool.
 20. The method ofclaim 18, wherein the particular pressure range includes sub-atmosphericpressure.